The invention relates to a mode selection control, and more particularly, to a vehicle steering mode selection control.
Various types of vehicles, including telescopic handler vehicles, or xe2x80x9ctelehandlersxe2x80x9d, have four wheel drive, four wheel Ackermann type steering and multiple steering modes. These steering modes can include a 4-wheel steering mode for tight situations (wherein the front wheels steer opposite to the rear wheels), a 2-wheel steering mode for road travel (wherein only the front wheels are steered), and a 4-wheel crab steer mode (wherein the front and rear wheels turn in the same direction) so that the vehicle moves in a different direction, but its orientation does not change.
Various apparatus and means for switching between these different steering modes are known. For example, it is known to use a solenoid operated three position valve to control fluid communication from a steering valve to the front and/or rear axle steering actuators. It is also known to use electrical switches to control the operation of the three position valve, and with such a system the operator may choose to look at the position of the wheels and switch between steering modes when the wheels are judged to be in a straight orientation. Some known production vehicles include a steering position sensor and illuminate a lamp on the operator console to provide the operator with information as to whether or not the wheels are straight. It is know to use sensors on both axles and two lamps, one for each axle.
It is also known to use various types of switches or control devices to switch between modes, the most common being a rocker or rotary switch. It is also known to use a separate switch to disable the indicator lamps when not in the process of switching between steering modes. Also known are automated systems which permit pre-selection of the desired steering mode, but wherein the steering mode is not actually changed until the wheels are steered to the center. With such automated systems, the operator is not provided with an indication of the position of the wheels.
There are certain problems associated with these known designs. For example, the steering mode can be accidentally or inadvertently changed by incidental contact with the switch. This could result in an undesired movement of the vehicle. Also, in the systems with the indicator lamps, the lamps are illuminated each time the wheels are steered through the straight ahead position. This illumination of the lamps is potentially distracting to the operator and does not provide any advantages during normal machine operation.
Accordingly, an object of this invention is to provide a vehicle steering mode selection control which prevents accidental or inadvertent changing of the steering mode.
A further object of the invention is to provide such a vehicle steering mode selection control which prevents unnecessary illumination of indicator lights.
These and other objects are achieved by the present invention, wherein a vehicle steering mode selection control includes a dual motion (push to turn) rotary switch which cooperates with a timer circuit, a lamp control unit, wheel alignment sensors, wheel alignment lamps, and a xe2x80x9csystem onxe2x80x9d lamp. To change modes, the operator pushes the switch so that it can be turned to select a different steering mode. Pushing the switch starts the timer, activates the wheel alignment sensors, activates or energizes the lamp control unit for a limited time period and illuminates the xe2x80x9csystem onxe2x80x9d lamp, indicating that the wheel alignment sensors and the lamp control unit are ready for use by the operator. When the wheels are steered to the centered or straight ahead position, the wheel alignment sensors and the lamp control unit cooperate to illuminate the corresponding wheel alignment lamps so that the operator can rotate the switch to change steering modes knowing that the wheels associated with the illuminated lamp are aligned straight. The timer provides a limited, pre-determined length of time for making the steering mode change with the assistance of the wheel alignment lamps. When the timer times out, all the wheel alignment lamps are kept off, but the operator can still change steering modes without the assistance of the wheel alignment lamps. If the operator chooses to push the switch and then immediately turn it to change the steering mode (without checking the status of the lamps), the system will immediately respond and change the steering mode as commanded. If timer times out before the switch is turned, the sensors and lamp control unit are de-activated, but the operator can still change steering modes without the assistance of the wheel alignment lamps.